Method for removing mercury from liquid hydrocarbon

ABSTRACT

A process for removing mercury of the present invention is characterized in that an ionic mercury-containing liquid hydrocarbon placed in a container equipped with a circulating means is effectively contacted with a sulfur compound represented by the general formula (I):  
     M 1 —S—M 2   (I)  
     wherein M 1  and M 2  may be the same or different and are each independently a hydrogen atom, an alkali metal or an ammonium group, by introducing the sulfur compound into a suction side and/or a discharge side of the circulating means while circulating the ionic mercury-containing liquid hydrocarbon into the container through the circulating means. By the process for removing mercury of the present invention, the ionic mercury is effectively removed from the liquid hydrocarbon in simple manner.

TECHNICAL FIELD

[0001] The present invention relates to a process for removing mercuryfrom a liquid hydrocarbon, and more particularly to an industriallyuseful process for removing an ionic mercury from an ionicmercury-containing liquid hydrocarbon placed in a container in a simpleand efficient manner.

BACKGROUND ART

[0002] As known in the art, natural gas liquid (NGL) recovered byremoving liquefied petroleum gas from natural gases obtained from gasfield contains mercury in an amount of from several tens to severalhundreds ppb although it varies depending upon the production area. Whensuch a liquid hydrocarbon containing mercury is used as a raw materialfor producing ethylene, etc., the activity of hydrogenation catalystsare reduced or the apparatus is corroded or it mechanical strength isreduced, because the mercury forms amalgams with platinum, palladium,copper or aluminum. For this reason, it has been strongly demanded todevelop a technique for removing mercury from the liquid hydrocarbon.

[0003] Japanese Patent Application Laid-Open No. 10-251667 proposes toremove mercury by using an apparatus comprising a hydrogenation zonehaving a packed bed of hydrogenation catalyst and an adsorption zonehaving a packed bed of porous carbonaceous material. In this method,after the hydrogenation process at 100 to 400° C., mercury is adsorbedonto activated carbon having strictly controlled properties such as aspecific surface area and a pore size. Therefore, the proposed method iscomplicated in its operation and has drawbacks of requiring acomplicated adsorbent preparation and strictly controlled operationconditions because of involving the adsorption process.

[0004] The inventors made various studies on a simple method of removingmercury from a mercury-containing liquid hydrocarbon, and found that themercury is effectively removed by ionizing the mercury in the liquidhydrocarbon and then contacting the ionized mercury with a specificsulfur compound.

DISCLOSURE OF INVENTION

[0005] It is an object of the present invention to provide anindustrially useful process for removing ionized mercury from an ionizedmercury-containing liquid hydrocarbon using a specific sulfur compoundin simple and effective manner.

[0006] As a result of extensive research in view of the above object,the inventors have found that the ionic mercury is effectively contactedwith the specific sulfur compound and effectively removed from the ionicmercury-containing hydrocarbon by circulating the ionicmercury-containing hydrocarbon into a container through a circulatingmeans while introducing the specific sulfur compound into a suction sideand/or discharge side of the circulating means with optional mechanicalstirring of the liquid hydrocarbon in the container. The presentinvention has been accomplished on the basis of this finding.

[0007] Thus, the present invention provides a process for removingmercury from a liquid hydrocarbon, which comprises a step of contactingan ionic mercury-containing liquid hydrocarbon placed in a containerwith a sulfur compound represented by the general formula (I):

M¹—S—M²  (I)

[0008] wherein M¹ and M² may be the same or different and are eachindependently a hydrogen atom, an alkali metal or an ammonium group,thereby removing the ionic mercury, wherein the container is equippedwith a circulating means for circulating the ionic mercury-containingliquid hydrocarbon into the container, and wherein the sulfur compoundis introduced into a suction side and/or a discharge side of thecirculating means while circulating the ionic mercury-containing liquidhydrocarbon through the circulating means. The ionic mercury-containingliquid hydrocarbon in the container may be mechanically stirred, ifdesired.

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] The ionized mercury-containing liquid hydrocarbons to be treatedby the process of the present invention are not particularly restricted,and may include any hydrocarbons which are liquid at ordinarytemperature.

[0010] Examples of the liquid hydrocarbons include crude oil, straightrun naphtha, kerosene, gas oil, vacuum distillates, topped crude, andnatural gas condensate (NGL). Of these liquid hydrocarbons, preferred isthe natural gas condensate.

[0011] The mercury contained in the liquid hydrocarbon may be in eitherof elementary form or ionic form. The elementary mercury is convertedinto the ionic form by the ionization treatment described later. Theconcentration of mercury of the liquid hydrocarbon to be treated is notparticularly restricted, and is usually 2 to 1,000 μg/L, preferably 5 to100 μg/L.

[0012] The crude oil to be treated in the present invention is notparticularly restricted. Examples of the crude oil are those produced inSaudi Arabia, United Arab Emirates, Nigeria, Canada, Mexico, Iran, Iraq,China, Kuwait, Malaysia, Venezuela, America, Australia, Russia, Libya,Philippines, Indonesia, Norway, Thai Land, Qatar, Argentina, England,and Japan. These crude oils may be used in combination of two or more.

[0013] The straight run naphtha, kerosene, gas oil, vacuum distillateand topped crude are obtained by processing the crude oil by knownmethods.

[0014] In the process of the present invention, the mercury contained inthe liquid hydrocarbon must be ionized before its removal from theliquid hydrocarbon. Although the ionization method is not particularlyrestricted, the elementary mercury may be ionized by contacting theliquid hydrocarbon with a substance capable of converting elementarymercury into ionic mercury. Examples of the mercury-ionizing substanceinclude an iron compound such as iron sulfate, iron chloride, ironsulfide, iron oxide and iron nitrate; a copper compound such as coppersulfate, copper chloride, copper oxide, copper nitrate and coppersulfide; a vanadium compound such as vanadium oxide, vanadium sulfideand vanadium sulfate; a manganese compound such as manganese oxide,manganese sulfide and manganese sulfate; a nickel compound such asnickel oxide, nickel sulfide and nickel sulfate; an inorganic peroxidesuch as hydrogen peroxide; an organic peroxide such as peracetic acid;atmospheric oxygen; and a crude oil tank sludge. These mercury-ionizingsubstances may be used alone or in combination of two or more. The crudeoil tank sludge is a settled sludge at the bottom of a crude oil tank,and contains elements such as Fe, Si, Na, Al, P, Zn, Cu, Ca, Mg, V, K,Cr, Mn, Ni, C, H, N, O and S.

[0015] The manganese compounds such as manganese oxide may be of anyshape such as powdery form, pulverized form, columnar form, sphericalform, fibrous form and honeycomb form. In addition, the manganesecompounds may be supported on a carrier such as silica, alumina,silica-alumina, zeolite, ceramic, glass, resin and activated carbon. Thesupporting amount is not particularly restricted, and is preferably 0.1to 30% by weight based on the weight of the carrier.

[0016] The conditions for ionizing the elementary mercury by contactingthe liquid hydrocarbon with the mercury-ionizing substance are notparticularly restricted. The ionization temperature is usually −50 to100° C., preferably 0 to 60° C. The ionization pressure may be notspecifically limited as far as the liquid hydrocarbon is maintained in aliquid state at the ionization temperature being used. Themercury-ionizing substance is used preferably in an amount of 1 to10,000 mol per one mole of the elementary mercury in the liquidhydrocarbon.

[0017] In the process of the present invention, the ionizedmercury-containing liquid hydrocarbon is received in a container andsubjected to a treatment for removing the ionized mercury. Examples ofthe container include a crude oil tank, a naphtha tank, a condensatetank, etc., although not limited thereto. Also, water may be present inthese containers.

[0018] The sulfur compound used for removing the ionic mercury from theliquid hydrocarbon is represented by the general formula (I):

M¹—S—M²  (I)

[0019] wherein M¹ and M² may be the same or different and are eachindependently a hydrogen atom, an alkali metal or an ammonium group.

[0020] Examples of the alkali metal for M¹ and M² of the formula (I)include sodium, potassium, lithium and cesium. Examples of the sulfurcompounds represented by the formula (I) include hydrogen sulfide,sodium sulfide, sodium hydrosulfide, potassium sulfide, potassiumhydrosulfide, ammonium sulfide, and ammonium hydrosulfide. These sulfurcompounds may be used alone or in combination of two or more. Of thesesulfur compounds, preferred are hydrogen sulfide, sodium sulfide andsodium hydrosulfide.

[0021] In the process of the present invention, the ionicmercury-containing liquid hydrocarbon fed into the container iscontacted with the sulfur compound of the formula (I) to convert theionic mercury to a solid mercury compound insoluble to the liquidhydrocarbon. Then, the solid mercury compound is removed from the liquidhydrocarbon by filtration, sedimentation, etc. To efficiently contactthe sulfur compound with the ionic mercury, the ionic mercury-containingliquid hydrocarbon in the container is circulated through a circulatingmeans, while introducing the sulfur compound to a suction side and/or adischarge side of the circulating means. The circulating means comprisesa pump which pumps up the liquid hydrocarbon by suction from thecontainer and discharges the pumped-up liquid hydrocarbon into thecontainer, and a conduit for passing through the liquid hydrocarbon.Generally, a suction inlet is disposed around the vicinity of thecontainer bottom, and a discharge outlet is disposed around the vicinityof the container top. The circulating rate is preferably 1 to 5,000m³/h.

[0022] Apart of an existing conduit for feeding the liquid hydrocarboninto the container or a part of an existing conduit for discharging theliquid hydrocarbon from the container may be used as the circulationconduit. Also, a circulation line usually used for separating water froma crude oil in the crude oil receiving for storage may be used as thecirculation conduit.

[0023] The form of the sulfur compound being introduced is notparticularly restricted. For example, when hydrogen sulfide is used asthe sulfur compound, it may be directly introduced in an inherentgaseous state or in the form of solution in water or a liquid organicsubstance such as naphtha, kerosene, light oil and heavy oil. When asulfur compound, such as sodium sulfide, which is solid at roomtemperature is used, the solid sulfur compound may be introduced in theform of an aqueous solution.

[0024] The supplied amount of the sulfur compound of the formula (I) is1 to 10,000 mol, preferably 100 to 5,000 mol per one mole of the mercurycontained in the liquid hydrocarbon. The total amount of the sulfurcompound is supplied over 1 to 300 h while circulating the liquidhydrocarbon. After supplying the total amount, the circulation of theliquid hydrocarbon is preferably continued for 1 to 300 h.

[0025] The conditions for the contact between the sulfur compound andthe ionic mercury are not particularly restricted. The contacttemperature is usually −50 to 100° C., preferably 0 to 60° C. Anysuitable pressure is usable as long as the liquid hydrocarbon ismaintained in a liquid state at the contact temperature being used.

[0026] In the process of the present invention, the contact between theionic mercury with the sulfur compound is further enhanced bymechanically stirring the liquid hydrocarbon in the container.

[0027] The present invention will be described in more detail byreference to the following examples. However, it should be noted thatthe following examples are illustrative and not intended to limit theinvention thereto.

EXAMPLE 1

[0028] Into a tank equipped with a circulation conduit, was fed 38,000m³ of a liquid hydrocarbon (density: 0.7363 g/cm³ at 15° C.) containing15.3 μg/L of ionic mercury. A pump with a capacity of 15 m³/h wasdisposed between the inlet and the outlet of the circulation conduit.Hydrogen sulfide was introduced at a feeding rate of 4.8 kg/h into asuction side of the pump while operating the pump. After introducinghydrogen sulfide over 21.4 h, the liquid hydrocarbon was furthercirculated for additional 24 h. During the circulation, the temperatureand pressure were controlled to 20° C. and ordinary pressure,respectively. Simultaneously with the circulation of the liquidhydrocarbon, the liquid hydrocarbon in the tank was stirred by astirrer.

[0029] The surface of the liquid hydrocarbon in the tank was 12 m highfrom the bottom of the tank. Immediately after stopping the stirring andcirculation of the liquid hydrocarbon, a portion of the liquidhydrocarbon was sampled from a position of 1 m high from the bottom. Thesampled liquid hydrocarbon was filtered through a filter of 0.5 μm poresize. The concentration of mercury of the resultant filtrate was 1 μg/L.

[0030] After 10 days from stopping the stirrer and the pump forcirculation, a portion of the liquid hydrocarbon was sampled at theposition of 1 m high from the bottom. The concentration of mercury ofthe sampled liquid hydrocarbon was 1 μg/L without filtration.

INDUSTRIAL APPLICABILITY

[0031] In accordance with the present invention, ionic mercury iseffectively removed from an ionic mercury-containing liquid hydrocarbonplaced in a container in extremely simple and industrially usefulmanner.

1. A process for removing mercury from a liquid hydrocarbon, whichcomprises a step of contacting an ionic mercury-containing liquidhydrocarbon placed in a container with a sulfur compound represented bythe general formula (I): M¹—S—M²  (i) wherein M¹ and M² may be the sameor different and are each independently a hydrogen atom, an alkali metalor an ammonium group, thereby removing the ionic mercury, wherein thecontainer is equipped with a circulating means for circulating the ionicmercury-containing liquid hydrocarbon into the container, and whereinthe sulfur compound is introduced into a suction side and/or a dischargeside of the circulating means while circulating the ionicmercury-containing liquid hydrocarbon through the circulating means. 2.The process according to claim 1, wherein the ionic mercury-containingliquid hydrocarbon in the container is mechanically stirred.
 3. Theprocess according to claim 1 or 2, wherein the sulfur compound is atleast one compound selected from the group consisting of hydrogensulfide, sodium sulfide, sodium hydrosulfide, potassium sulfide,potassium hydrosulfide, ammonium sulfide, and ammonium hydrosulfide. 4.The process according to any one of claims 1 to 3, wherein the liquidhydrocarbon is circulated at a rate of 1 to 5000 m³/h.
 5. The processaccording to any one of claims 1 to 4, wherein the sulfur compound isintroduced in an amount of 1 to 10,000 mol per one mole of mercurycontained in the liquid hydrocarbon.
 6. The process according to any oneof claims 1 to 5, wherein 1 to 10,000 mol of the sulfur compound per onemole of mercury contained in the liquid hydrocarbon is introduced over 1to 300 h.
 7. The process according to any one of claims 1 to 6, whereinthe liquid hydrocarbon is further circulated for additional 1 to 300 hafter introducing the sulfur compound.